1. Field of the Invention
The field of the invention is that of deformable microstructures with two-directional operation, particularly that of accelerometers comprising a moving mass connected to a fixed frame via slender suspension arms.
2. Discussion of the Background
The accelerations experienced by the moving mass may typically be detected thanks to the presence of piezoresistive gauges on the slender suspension arms. Such piezoresistive gauges may also control an electromagnetic device for controlling the moving mass, in order to compensate for its displacements.
In this case, the accelerometer strain gauges are intended to generate, by means of an electronic circuit, a supply current for a coil which, using phenomena of electromagnetic induction, compensates for a displacement of the moving mass under the effect of external conditions, for example seismic movements.
At the present time, such accelerometers can be built using silicon wafers, using silicon etching techniques developed in the context of the manufacture of semiconductor electronic components. The use of such technologies allows the moving mass and the elements associated with it to be produced by a collective process on slices of silicon and thus allows a series of acceleration sensors to be defined, using a limited number of technological steps.
Typically, the manufacture of this type of sensor comprises assembling several silicon wafers, at least one central wafer in which the moving mass is produced, and two outer wafers having stop elements for the moving mass, thus making it possible to limit the amplitude of the movements which the said moving mass can be made to experience, and thus to optimize the protection of the moving mass and of the suspension arms. An example of an accelerometer made up of at least three silicon wafers according to the known art is illustrated in FIG. 1.
More specifically, FIG. 1 illustrates a cross-section through this type of accelerometer the manufacture of which is, in particular, the result of assembling 4 silicon wafers, a so-called upper wafer constituting part of the fixed frame and comprising upper stops Bs, two central wafers constituting the moving mass 1 and part of the fixed frame and a fourth wafer, called the lower wafer, comprising part of the fixed frame and a stop plane Bi for the lower face of the moving mass.
To simplify the architecture of this type of accelerometer and make the method of manufacturing it easier, accelerometers are known which result from assembling two wafers in which all the elements and functions are defined (moving mass, suspension arms, frame) as disclosed in Application WO 95/04284 or U.S. Pat. No. 5,121, 633.